HIV disease is characterized by high level CD8+ T cell activation and impairment in T cell function. Despite being the distinguishing characteristic of HIV-1 infection, the basis for the variation in CD8+ T cell activation in humans is not well understood. Variation in circulating strains of HIV-1 may account for this variation. We intend to map viral genetic determinants of T cell activation within the HIV-1 Nef protein. The HIV-1 Nef protein has been repeatedly implicated in manipulation of the human immune system. Adopting a very wide array of functions, HIV-1 Nef down modulates expression of key surface receptors, such as CD4, CD28, and MHC, facilitates viral entry and release, directly interacts with signaling proteins, such as the T cell receptor proximal kinase, Lck, and induce IL-2 expression. The sites c [unreadable] onferring these functions to Nef fall in distinct regions of the protein - regions which vary in sequence across HIV-1 strains. Nef is expressed early in infection, and is a target for CTL immune escape. HIV-1 Nef activity within infected CD4+ T cells influences cellular response to stimuli, cytokine secretion patterns, and interaction with CD8+ T cells. In this way, Nef may influence CD8+ T cell activation levels and T cell maturation. While Nef has been studied extensively in vitro, the impact of Nef sequence variation in vivo has not been well studied. We propose to relate HIV-1 viral nef sequence to T cell activation levels, T cell phenotype, and T cell signaling alterations by use of advanced bioinformatic mapping tools. We will perform these studies in a cohort of 220 recently HIV-1 infected adults with well-characterized disease course and in collaboration with the UCSF/CFAR Core Immunology Laboratory and the UCSF Laboratory of Clinical Virology. We will use tree- structured biostatistical methods and their extensions which are well suited to handling of high-dimensional biological data types, such as genetic sequence and flow cytometry. The strengths of this application include the availability of specimens from a well-characterized cohort of HIV-1 infected adults; the use of advanced bioinformatic mapping tools; high-dimensional flow cytometric measures of function and signaling; a highly qualified inter-disciplinary research team; and a longitudinal approach to study of a genetically diverse entity, HIV-1. This work will facilitate development of therapies to improve the effectiveness of T cell responses and design of an effective HIV vaccine. HIV disease is characterized by high level CD8+ T cell activation and impairment in T cell function. Despite being the distinguishing characteristic of HIV-1 infection, the basis for the variation in CD8+ T cell activation in humans is not well understood. Variation in circulating strains of HIV-1 may account for this variation. We intend to map viral genetic determinants of T cell activation within the HIV-1 Nef protein. [unreadable] [unreadable] [unreadable]